1. Field of the Invention
This invention relates to an apparatus for producing hydrogen, and in particular to a compact methanol-steam reformer.
The initial commercial sales of fuel cells will most likely be to a niche market of small off-grid power applications. These applications are characterised by a need for reliable, efficient and compact yet portable systems. The cell technology receiving the most industrial attention is the polymer electrolyte fuel cell (PEFC); the susceptibility of the PEFC anode to CO poisoning necessitates a nearly pure hydrogen source as fuel. Significant loss in PEFC efficiency can be observed with anode CO concentrations as low as 20 ppm.
An alternative to compressed hydrogen gas storage is a liquid fuel processing system. A recent study (Pattersson, L. F. et al, International Journal of Hydrogen Energy, Vol. 26, 2001) indicates that gasoline and methanol are prime candidates for near-term fuels in reforming processes. The advantages of methanol through its relatively simple kinetics, low reforming temperature and high hydrogen yield outweigh its disadvantage in a lack of distribution infrastructure particularly for non-permanent and portable applications.
2. Discussion of the Prior Art
Indeed, there has been a great deal of activity in the area of methanol-steam reforming apparatuses. In this connection, reference is made to Canadian Patents Nos. 1,288,596, issued to D. F. Szydlowski et al on Sep. 10, 1991 and 2,118,956, issued to Y. Shirasaki et al on Aug. 25, 1998, laid open Canadian Applications Nos. 2,274,904, filed by D. J. Edlund et al on Oct. 14, 1998; 2,307,971, filed by M. Iijima, et al on May 9, 2000; 2,310,928, filed by K. Kobayashi et al on Jun. 5, 2000; 2,323,660, filed by K. M. Vanden Bussche et al on Oct. 18, 2000; 2,345,966, filed by D. J. Edlund et al on Apr. 14, 1999; 2,351,867, filed by T. Seki et al on Jun. 26, 2001 and 2,357,960, filed by T. Miura et al on Sep. 28, 2001, U.S. Pat. No. 3,144,312, issued to C. Mertens on Aug. 11, 1964; U.S. Pat. No. 3,350,176, issued to R. B. Green et al on Oct. 31, 1967; U.S. Pat. No. 4,692,306, issued to R. G. Minet et al on Sep. 8, 1987; U.S. Pat. No. 4,861,347, issued to D. F. Szydlowski et al on Aug. 29, 1989; U.S. Pat. No. 5,226,928, issued to T. Makabe et al on Jul. 13, 1993; U.S. Pat. No. 5,639,431, issued to Y. Shirasaki et al on Jun. 17, 1997; U.S. Pat. No. 5,932,181, issued to T. C. Kim et al on Aug. 3, 1999; U.S. Pat. No. 5,997,594, issued to D. J. Edlund et al on Dec. 7, 1999; U.S. Pat. No. 6,162,267, issued to J. W. Priegnitz et al on Dec. 19, 2000; U.S. Pat. No. 6,221,117, issued to D. J. Edlund et al on Apr. 24, 2001 and U.S. Pat. No. 6,413,479, issued to H. Kudo et al on Jul. 2, 2002, and laid open US Applications Nos. 2002/0011152, filed in the name of M. Oku et al on Jun. 25, 2001 and 2002/0172630, filed in the name of S. Ahmed et al on Mar. 21, 2001.
In general, existing apparatuses have separate reforming and purification sub-systems which results in an overall apparatuses of significant size. While systems combining the reforming and purification processes have been proposed, it is common to encounter heat transfer problems because of the highly endothermic nature of the reaction network which necessitates a large heat transfer area. Thus, a need still exists for a system which minimizes size while maximizing heat transfer areas.